Numerous oxidizing organic compounds which are present in photographic elements are known, including, for example, quinones, anthraquinones, nitro compounds, tetrazolium compounds, phenazine derivatives, phenazine oxide derivatives, bipyridyl quaternary salt derivatives, etc. These are described, for example, in Japanese Patent Application (OPI) No. 45718/74 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), British Patent No. 956,277, U.S. Pat. Nos. 3,449,122 and 3,396,023, Japanese Patent Application (OPI) No. 64839/84, West German Patent Application (OLS) No. 2,734,335, etc. These oxidizing compounds are in most cases used as an antifoggant, desensitizer, contrast enhancer, etc. In preparation of silver halide photographic materials with less fog, these known compounds are often tested widely so as to obtain the intended photographic characteristic. The reason is as follows: Even the same oxidizing compound displays an extremely different effect when the formulation of the silver halide emulsion containing the oxidizing compound differs, and so it is seldom that the intended object could be attained. Moreover, even if the intended object could be attained, the compound incorporated into the material would often have various problematic properties that the compound would be rendered unfavorable for preparation of silver halide photographic materials. Often the compound has adverse side effects to the photographic characteristics (for example, noticeable desensitization). The compound frequently has an adverse influence on the storability. Another problem is that the compound can cause coloration or staining of the material. Often the compound, which is dissolved in the developer used for processing the material, precipitates out of solution, and the resulting precipitate has a harmful influence on the developer.
Moreover, to date there is much that is unknown about these oxidizing compounds. For example, the mechanism for the object of the use of the compounds has yet to be clarified. Likewise, the relation between the physical properties of the oxidizing compounds and those of silver halide emulsions is still unclear. Thus, under the existing state of knowledge, it is still extremely difficult to determine which oxidizing compounds are effective.
A phenomenon of so-called "black spots" is known in the field of photographic light-sensitive materials for graphic arts. This phenomenon is similar to that of fog in silver halide photographic materials. The phenomenon of black spots also have various unclarified problems, and the solution of such problems has also been desired.
Because of the above-mentioned reasons, it is preferable to select oxidizing compounds capable of attaining a desired characteristic from numerous kinds of various compounds in the preparation of silver halide photographic materials. Thus, it is further preferable to determine the effect and mechanism of various oxidizing compounds in various silver halide photographic materials so that the search for more effective oxidizing compounds can be advanced.